Humboldt State University ® Department of Chemistry

Robert A. Paselk Scientific Instrument Museum

 
From: Duff, A. Wilmer, A Text-Book of Physics, 5th ed., P. Blakiston's Son & Co., Philadelphia (1921) pp. 154-5.
 
© Copyright 1998 R. Paselk
 

 
 
225. Manometers. - A manometer is an apparatus for measuring the pressure of a fluid. In the simplest form the pressure to be measured is balanced against the pressure of a column of liquid in a tube. This is called the open tube manometer or siphon gauge. The pressure is found from the difference of level of the liquid in the two arms and the density, p, of the liquid. In absolute units of force P = gph + atmospheric pressure, while in the weight of unit mass as unit of force P = ph + atmospheric pressure (Fig. 126).
 
In another manometer the pressure to be measured is balanced against that of a gas (usually air) in a uniform closed tube. By Boyle's Law the pressure in the gas is inversely as the volume, that is, inversely as the length of the air column. The pressure in the gas plus that indicated by the difference of level of the liquid is the pressure to be measured (Fig. 127).


 

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